The present invention relates to a compressor for use in an air conditioner for vehicle, especially, a piston type compressor in which the rotation of the piston is prevented.
Conventionally, it is common that a rotation preventing member and the piston are formed integrally. For example, devices in FIG. 7 and FIG. 8(a) are disclosed in Japanese Unexamined Patent Publication No. 11-201037.
A drive shaft 101 is rotatably supported by a housing 102. A swash plate 13 as a cam plate is coupled with the drive shaft 101 to rotate integrally. A cylinder bore 102a is defined in the housing 102. A head portion 104a of a single-headed piston 104 is inserted into the cylinder bore 102a. A neck portion 104b of the piston 104 is arranged outside of the cylinder bore 102a. A pair of shoe seats or semi-spherical recesses 104c is inwardly recessed to define pockets in the neck portion 104b of the piston 104. A pair of shoes 105 is arranged in the neck portion 104b of the piston 104, and received by the shoe seats 104c. The peripheral portions of the swash plate 103 are slidably sandwiched between the shoes 105. The rotational movement of the swash plate 103 accompanying with the rotation of the drive shaft 101 is converted to the reciprocating movement of the piston 104 through the shoes 105. Then the compression cycle is performed such that a refrigerant gas is sucked into the cylinder bore 102a, compressed and discharged out.
A piston 104 is provided with a rotation preventing portion 106. The piston 104 and the rotation preventing portion 106 are formed integrally. The rotation preventing portions 106 are formed on the neck portion 104b of the piston 104 so as to protrude ahead and behind in the rotational direction of the swash plate 103, respectively. The rotation preventing portions 106 are formed such that the curvature of contacting surfaces 106a confronting a contacting portion 102b of the housing 102 is smaller than that of the head portion 104a. An axis of an arc of the rotation preventing portion 106 is different from that of an arc of the head portion 104a. The housing 102 and the piston 104 are made of aluminium or an aluminium alloy for reducing its weight. A coating layer is formed on the head portion 104a and the contacting surface 106a for preventing seizure between the housing 102 and the piston 104 and for improving wearproof of the piston 104. The contacting portion 102b prevents the rotation of the piston, cooperating with the rotation preventing portion 106.
The connecting structure between the piston 104 and the swash plate 103 through the shoes 105 allows the rotation around the axis S of the piston 104. If the piston 104 rotates significantly, the neck portion interferes with the rotating swash plate 103 and there is a possibility of causing vibration and noise. However, as shown in FIG. 8(a) as two dotted chain line, the amount of rotation of the piston 104 could be reduced by that one end of the rotation preventing portion 106 contacts with the contacting portion 102b. Therefore, the piston 104 does not interfere with the swash plate 103.
On the other hand, another type of compressor, in which the rotation preventing member and the piston are arranged separately, is disclosed in Japanese Unexamined Patent Publication No. 9-105377.
As shown in FIG. 8(b) and FIG. 9, a protruding portion 111 is formed on the end portion of the piston 110. The intermediate portion of an arched leaf spring 112 is fastened to the protruding portion 111 with a screw 113. As shown in FIG. 8(b), the leaf spring 112 is assembled such that both end portions 112a are pressed to the inner wall surface 114a of the cylinder block (housing) 114, slidably in the moving direction of the piston 110, respectively.
Generally, a piston is produced by performing machining process, coating process to form a coating layer to cover the surface, and polishing process etc. to the material formed by molding or forging. As the piston 104 disclosed in Japanese Unexamined Patent publication No. 11-201037, it becomes troublesome to machine the piston or form a coating layer on the piston by roll coating, for the rotation preventing portion 106 and the piston 104 are formed integrally and the axis of the arc of the rotation preventing portion 106 deviates from that of the arc of the contacting surface 106a. 
On the other hand, a compressor disclosed in Japanese Unexamined Patent Publication No. 9-105377 has the following problems.
(1) The rotation prevention of the piston 110 is performed by the leaf spring 112 which is continually press-contacted to the inner wall surface 114a of the housing 114, and an unbalanced load is continually affected to a piston 110 from the leaf spring 112. Therefore, the inner wall surface 114a of the housing 114 to which the leaf spring 112 is press-contacted, is easily worn, and then the piston 110 is easily worn partially. To control the amount of rotation of the piston 110 under a required quantity, it needs to strengthen the spring force of the leaf spring 112. However, that makes the above problem remarkable.
(2) The protruding portion 111 is formed on the end portion of the piston 110 and the leaf spring 112 is fastened to it with the screw 113. Such a structure axially lengthen the piston 110 and increases the size of the compressor. Furthermore, it needs to machine the screw 113 and a tapped hole 115, and increases the manufacturing process.
The present invention was achieved by recognizing the above problems in the prior art. The purpose is to propose a compressor in which the rotation of the piston is prevented without affecting a big unbalanced load to the piston and the manufacture for the piston is simplified.
A piston type compressor comprises a housing having a cylinder bore therein, a drive shaft rotatably supported in the housing, a cam plate coupled on the drive shaft to rotate integrally therewith, a piston being operatively connected to the cam plate through a pair of shoes, the piston including a head portion and a neck portion, the head portion of the piston being inserted into the cylinder bore, and the cam plate converting rotation of the drive shaft to reciprocating movement of the piston through the pair of shoes. In the above compressor, the present invention has the following features. A rotation preventing member is formed separately from the piston and mounted on the piston. A contacting portion is formed in the housing. The rotation preventing member prevents rotation around the axis of the piston, by contacting with the contacting portion when the piston rotates by a certain angle.
According to the present invention, it is easy to machine the piston and to form a coating layer on the piston by roll coating etc., for the rotation preventing member is formed separately from the piston. During the running of the compressor, a moment around the axis of the piston acts to the piston, accompanied with the rotation of the swash plate, and the piston tends to rotate around the axis. However, when the piston rotates by a certain angle from the base portion, the rotation is prevented, for the rotation preventing member contacts the contacting portion. Therefore, the piston slides without receiving an unbalanced load, different from the structure that a leaf spring is used as the rotation preventing member.
Furthermore, the present invention has a following feature. The rotation preventing member is received in the piston. A stopper for preventing the relative movement of the rotation preventing member in the axial direction of the piston is arranged between the rotation preventing member and the piston. Accordingly, even after long use, the rotation preventing member is not separated from the piston by slipping in the axial direction of it.
Furthermore, the present invention has a following feature. The rotation preventing member is provided with a rotation preventing portion to prevent the rotation in both directions around the axis of the piston. Accordingly, one rotation preventing member can prevent the piston from rotating in both directions.
Furthermore, the present invention has a following feature. The above rotation preventing member is made of a different material from that of the housing. Accordingly, it does not need to form a coating on the rotation preventing member for avoiding the seizure, and then it is manufactured easily.